Melt processable starch compositions

ABSTRACT

The present invention relates to a starch composition comprising starch, a polymer that is substantially compatible with starch and has a weight-average molecular weight of at least 500,000 such that the polymer forms effective entanglements or associations with neighboring starch molecules, and preferably at least one additive to improve melt flow and melt processability. The additive may be a hydroxyl plasticizer, a hydroxyl-free plasticizer, a diluent, or mixtures thereof. The composition is melt processable on conventional thermoplastic equipment. The composition is especially suitable for uniaxial and biaxial extensional processes to make fibers, films, foams and like products.

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of Ser. No. 09/914,965 filedSep. 6, 2001 which is a 371 application of International ApplicationPCT/IB00/00233 filed Mar. 7, 2000 which is a continuation-in-partapplication of Ser. No. 09/264,401 filed Mar. 8, 1999, abandoned.

FIELD OF INVENTION

[0002] This invention relates a novel starch composition that issubstantially homogenous and has desirable rheological characteristicssuch that it is melt processable by conventional thermoplasticprocessing equipment. The present composition is particularly suitablefor uniaxial and biaxial extensional processes.

BACKGROUND OF THE INVENTION

[0003] It is well recognized that starch molecules come in two forms:the substantially linear amylose polymer and the highly branchedamylopectin polymer. These two forms of starch have very differentproperties, probably due to the ease of association of the hydroxylgroups among different molecules. The molecular structure of amylose isessentially linear with two to five relatively long branches. Theaverage degree of polymerization of the branches is about 350 monomerunits. Under conditions that provide sufficient freedom of molecularmovements, primarily by dilution with suitable solvents, and in someinstances, dilution coupled with heating, the linear amylose chains canbe oriented into preferentially parallel alignments such that thehydroxyl groups on one chain are in close proximity with those on theadjacent chains. The alignment of neighboring amylose molecules isbelieved to facilitate intermolecular hydrogen bonding. Consequently theamylose molecules form strong aggregates. In contrast, the molecularstructure of amylopectin is highly branched via 1,6-α linkages. Theaverage degree of polymerization of the branches is about 25 monomerunits. Due to the highly branched structure, the amylopectin moleculescan not move as freely and do not align and associate as readily.

[0004] Attempts have been made to process natural starch on standardequipment and existing technology known in the plastic industry. Sincenatural starch generally has a granular structure, it needs to be“destructurized” and/or modified before it can be melt processed like athermoplastic material. For destructurization, the starch is typicallyheated above its softening and melting temperature under a pressurizedcondition. Melting and disordering of the molecular structure of thestarch granule takes place and a destructurized starch is obtained.Chemical or enzymatic agents may also be used to destructurize, oxidize,or derivatize the starch. Modified starches have been used to makebiodegradable plastics, wherein the modified starch is blended as anadditive or the minor component with petroleum-based or syntheticpolymers. However, when the modified starch is processed by itself or asthe major component in a blend with other materials using conventionalthermoplastic processing techniques, such as molding or extrusion, thefinished parts tend to have a high incidence of defects. Moreover, themodified starch (alone or as the major component of a blend) has beenfound to have poor melt extensibility; consequently, it cannot besuccessfully processed by uniaxial or biaxial extensional processes intofibers, films, foams or the like.

[0005] Previous attempts to produce starch fibers relate principally towet-spinning processes. For Example, a starch/solvent colloidalsuspension can be extruded from a spinneret into a coagulating bath.This process relies on the marked tendency of amylose to align and formstrongly associated aggregates to provide strength and integrity to thefinal fiber. Any amylopectin present is tolerated as an impurity thatadversely affects the fiber spinning process and the strength of thefinal product. Since it is well known that natural starch is rich inamylopectin, earlier approaches include pre-treating the natural starchto obtain the amylose-rich portion desirable for fiber spinning. Clearlythis approach is not economically feasible on a commercial scale since alarge portion (i.e, the amylopectin portion) of the starch is discarded.In more recent developments, natural starch, typically high in naturalamylopectin content, can be wet-spun into fibers. However, the wet-spunfibers are coarse, typically having fiber diameters greater than 50microns. Additionally, the large quantity of solvent used in thisprocess requires an additional drying step and a recovery or treatmentstep of the effluent. Some references for wet-spinning starch fibersinclude U.S. Pat. No. 4,139,699 issued to Hernandez et al. on Feb. 13,1979; U.S. Pat. No. 4,853,168 issued to Eden et al. on Aug. 1, 1989; andU.S. Pat. No. 4,234,480 issued to Hernandez et al. on Jan. 6, 1981.

[0006] U.S. Pat. Nos. 5,516,815 and 5,316,578 to Buehler et al. relateto starch compositions for making starch fibers from a melt spinningprocess. The melt starch composition is extruded through a spinneretteto produce filaments having diameters slightly enlarged relative to thediameter of the die orifices on the spinnerette (i.e., a die swelleffect). The filaments are subsequently drawn down mechanically orthermomechanically by a drawing unit to reduce the fiber diameter. Themajor disadvantage of the starch composition of Buehler et al. is thatit does not use high molecular weight polymers, which enhance the meltextensibility of starch compositions. Consequently, the starchcomposition of Buehler et al. could not be successfully melt attenuatedto produce fine fibers of 25 microns or less in diameter.

[0007] Other thermoplastically processable starch compositions aredisclosed in U.S. Pat. No. 4,900,361, issued on Aug. 8, 1989 to Sachettoet al.; U.S. Pat. No. 5,095,054, issued on Mar. 10, 1992 to Lay et al.;U.S. Pat. No. 5,736,586, issued on Apr. 7, 1998 to Bastioli et al.; andPCT publication WO 98/40434 filed by Hanna et al. published Mar. 14,1997. These starch compositions do not contain the high molecular weightpolymers that are necessary to achieve the desired melt viscosity andmelt extensibility, which are critical material characteristics toproducing fine fibers, thin films or thin-walled foams.

[0008] The art shows a need for an inexpensive and melt processablecomposition from natural starches. Such a melt processable starchcomposition should not require evaporation of a large quantity ofsolvents or produce a large amount of effluent during the processingoperation. Moreover, such a starch composition should have meltrheological properties suitable for use in conventional plasticprocessing equipment The art also shows a need for a starch compositionsuitable for use in uniaxial or biaxial extensional processes to producefibers, films, sheets, foams, shaped articles, and the like economicallyand efficiently. Specifically, the starch composition should have meltrheological properties suitable for uniaxial or biaxial extensionalprocesses in its melt phase in a substantially continuous manner, i.e.,without excessive amount of melt fracture or other defects.

SUMMARY OF THE INVENTION

[0009] The present invention relates to a starch composition that ismelt processable on conventional thermoplastic equipment. Specifically,the starch composition may be successfully processed via uniaxial orbiaxial extensional forces to provide a final product with goodstrength. Moreover the starch composition has rheological propertiessuitable for use in melt attenuation processes to achieve very highuniaxial or biaxial extensions, which are generally not achievable byother processes, including jet or mechanical elongation processes.

[0010] The present invention relates to a starch composition comprisingstarch, a polymer that is substantially compatible with starch and has amolecular weight sufficiently high to form effective entanglements orassociations with neighboring starch molecules, and preferably at leastone additive to improve melt flow and melt processability. Polymershaving a weight-average molecular weight of at least 500,000 areparticularly useful herein. The additive may be a hydroxyl plasticizer,a hydroxyl-free plasticizer, a diluent, or mixtures thereof.

[0011] The starch compositions of the present invention have thecombination of melt strength and melt viscosities (shear andextensional) in the desired range such that the compositions areuniquely suitable for the melt extensional processes. The starchcomposition of the present invention typically has a melt shearviscosity in the range of about 0.1 to about 40 Pa·s so that thecomposition can be mixed, conveyed or otherwise processed onconventional processing equipment, including screw extruders, stirtanks, pumps, spinnerets, and the like. The starch composition of thepresent invention typically has an enhanced melt extensional viscositydue to the incorporation of the high polymers.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]FIG. 1 shows a torque rheometer assembly having a melt blowing dieused to produce fine starch fibers of the present invention.

[0013]FIG. 2 shows a torque rheometer assembly used to produce starchfiber web by spun bonding.

[0014]FIG. 3a is the Scanning Electron Micrographs of fine starch fibersof the present invention shown on a 200 micron scale.

[0015]FIG. 3b is the Scanning Electron Micrographs of fine starch fibersof the present invention shown on a 20 micron scale.

DETAILED DESCRIPTION OF THE INVENTION

[0016] As used herein, the term “comprising” means that the variouscomponents, ingredients, or steps, can be conjointly employed inpracticing the present invention. Accordingly, the term “comprising”encompasses the more restrictive terms “consisting essentially of” and“consisting of.”

[0017] As used herein, the term “bound water” means the water foundnaturally occurring in starch and before starch is mixed with othercomponents to make the composition of the present invention. The term“free water” means the water that is added in making the composition ofthe present invention. A person of ordinary skill in the art wouldrecognize that once the components are mixed in a composition, water canno longer be distinguished by its origin.

[0018] All percentages, ratios and proportions used herein are by weightpercent of the composition, unless otherwise specified.

[0019] The Starch Compositions

[0020] Naturally occurring starch is generally a mixture of linearamylose and branched amylopectin polymer of D-glucose units. The amyloseis a substantially linear polymer of D-glucose units joined by (1,4)-α-Dlinks. The amylopectin is a highly branched polymer of D-glucose unitsjoined by (1,4)-α-D links and (1,6)-α-D links at the branch points.Naturally occurring starch typically contain relatively highamylopectin, for example, corn starch (64-80% amylopectin), waxy maize(93-100% amylopectin), rice (83-84% amylopectin), potato (about 78%amylopectin), and wheat (73-83% amylopectin). Though all starches areuseful herein, the present invention is most commonly practiced withhigh amylopectin natural starches derived from agricultural sources,which offer the advantages of being abundant in supply, easilyreplenishable and inexpensive.

[0021] Suitable for use herein are any naturally occurring unmodifiedstarches and modified starches; the starch may be modified by physical,chemical, or biological processes, or combinations thereof. The choiceof unmodified or modified starch for the present invention may depend onthe end product desired. Also suitable for use herein are mixtures ofvarious starches, as well as mixtures of the amylose or amylopectinfractions, having an amylopectin content in the desirable range. Thestarch or starch mixture useful in the present invention typically hasan amylopectin content from about 20% to about 100%, preferably fromabout 40% to about 90%, more preferably from about 60% to about 85% byweight of the starch or mixtures thereof.

[0022] Suitable naturally occurring starches can include, but are notlimited to, corn starch, potato starch, sweet potato starch, wheatstarch, sago palm starch, tapioca starch, rice starch, soybean starch,arrow root starch, amioca starch, bracken starch, lotus starch, waxymaize starch, and high amylose corn starch. Naturally occurring starchesparticularly, corn starch and wheat starch, are the preferred starchpolymers due to their economy and availability.

[0023] Physical modifications of the starch may be intramolecular orintermolecular modifications. Intramolecular modifications includereduced molecular weight and/or molecular weight distribution, changesin the polymer chain conformation, and the like. Intermolecularmodifications include melting and/or disordering the starch molecules,reduction in crystallinity, crystallite size, and granular size, and thelike. These physical modifications may be achieved by input of energy(such as thermal, mechanical, thermomechanical, electromagnatic,ultrasonic, and the like), pressure, moisture, fractionation, andcombinations thereof.

[0024] Chemical modifications of starch typically include acid or alkalihydrolysis and oxidative chain scission to reduce molecular weight andmolecular weight distribution. Suitable compounds for chemicalmodification of starch include organic acid such as citric acid, aceticacid, glycolic acid, and adipic acid; inorganic acids such ashydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, boricacid, and partial salts of polybasic acids, e.g., KH₂PO₄, NaHSO₄; groupIa or IIa metal hydroxides such as sodium hydroxide, and potassiumhydroxide; ammonia; oxidizing agents such as hydrogen peroxide, benzoylperoxide, ammonium persulfate, potassium permagnate, sodium bicarbonate,hypochloric salts, and the like; and mixtures thereof. Preferredchemical agents of the present invention include ammonium persulfate,sulfuric acid, hydrochloric acid, and mixtures thereof.

[0025] Chemical modifications may also include derivatization of starchby reaction of its OH groups with alkylene oxides, and other ether-,ester-, urethane-, carbamate-, or isocyanate-forming substances.Hydroxylalkyl, acetyl, or carbamate starches or mixtures thereof arepreferred chemically modified starches. The degree of substitution ofthe chemically modified starch is 0.05 to 3.0, preferably 0.05 to 0.2.

[0026] Biological modifications of starch include bacterial digestion ofthe carbohydrate bonds, or enzymatic hydrolysis using enzymes such asamylase, amylopectase, and the like.

[0027] The starch typically has a bound water content of about 5% to 16%by weight of starch. A water content of about 8% to about 12% by weightof starch is particularly preferred. The amylose content of the starchis typically from 0% to about 80%, preferably from about 20% to about35%, by weight of starch.

[0028] Natural, unmodified starch generally has a very high averagemolecular weight and a broad molecular weight distribution (e.g. naturalcorn starch has an average molecular weight of about 10,000,000 and amolecular weight distribution greater than 1000). The average molecularweight of starch can be reduced to the desirable range for the presentinvention by chain scission (oxidative or enzymatic), hydrolysis (acidor alkaline catalyzed), physical/mechanical degradation (e.g., via thethermomechanical energy input of the processing equipment), orcombinations thereof. These reactions also reduce the molecular weightdistribution of starch to less than about 600, preferably to less thanabout 300. The thermomechanical method and the oxidation method offer anadditional advantage in that they are capable of being carried out insitu of the melt spinning process.

[0029] In one embodiment, the natural starch is hydrolyzed in thepresence of acid, such as hydrochloric acid or sulfuric acid, to reducethe molecular weight and molecular weight distribution. In anotherembodiment, a chain scission agent may be incorporated into the meltspinnable starch composition such that the chain scission reaction takesplace substantially concurrently with the blending of the starch withother components. Nonlimiting examples of oxidative chain scissionagents suitable for use herein include ammonium persulfate, hydrogenperoxide, hypochlorate salts, potassium permanganate, and mixturesthereof. Typically, the chain scission agent is added in an amounteffective to reduce the weight-average molecular weight of the starch tothe desirable range. For example, it is found that for uniaxial orbiaxial melt attenuation processes, the starch should have aweight-average molecular weight ranging from about 1,000 to about2,000,000, preferably from about 1,500 to about 800,000, more preferablyfrom about 2,000 to about 500,000. It is found that compositions havingmodified starch in the above molecular weight range have a suitable meltshear viscosity, and thus improved melt processability. The improvedmelt processability is evident in less interruptions of the process(e.g., reduced breakage, shots, defects, hang-ups) and better surfaceappearance and strength properties of the product.

[0030] Typically the composition herein comprises from about 20 to about99.99 wt %, preferably from about 30 to about 95 wt %, and morepreferably from about 50 to about 85 wt %, of unmodified and/or modifiedstarch. The weight of starch in the composition includes starch and itsnaturally occurring bound water content. It is known that additionalfree water may be incorporated as the polar solvent or plasticizer, andnot included in the weight of the starch.

[0031] High molecular weight polymers (hereinafter “high polymers”)which are substantially compatible with starch are also useful herein.The molecular weight of a suitable polymer should be sufficiently highto effectuate entanglements and/or associations with starch molecules.The high polymer preferably has a substantially linear chain structure,though a linear chain having short (C1-C3) branches or a branched chainhaving one to three long branches are also suitable for use herein. Asused herein, the term “substantially compatible” means when heated to atemperature above the softening and/or the melting temperature of thecomposition, the high polymer is capable of forming a substantiallyhomogeneous mixture with the starch (i.e., the composition appearstransparent or translucent to the naked eye).

[0032] The Hildebrand solubility parameter (δ) can be used to estimatethe compatibility between starch and the polymer. Generally, substantialcompatibility between two materials can be expected when theirsolubility parameters are similar. It is known that water has aδ_(water) value of 48.0 MPa^(1/2), which is the highest among commonsolvents, probably due to the strong hydrogen bonding capacity of water.Starch typically has a δ_(starch) value similar to that of cellulose(about 34 MPa^(1/2)).

[0033] Without being bound by theory, it is believed that polymerssuitable for use herein preferably interact with the starch molecules onthe molecular level in order to form a substantially compatible mixture.The interactions range from the strong, chemical type interactions suchas hydrogen bonding between polymer and starch, to merely physicalentanglements between them. The polymers useful herein are preferablyhigh molecular weight, substantially linear chain molecules. The highlybranched structure of a amylopectin molecule favors the branches tointeract intramolecularly, due to the proximity of the branches within asingle molecule. Thus, it is believed that the amylopectin molecule haspoor or ineffective entanglements/interactions with other starchmolecules, particularly other amylopectin molecules. The compatibilitywith starch enables suitable polymers to be intimately mixed andchemically interact and/or physically entangle with the branchedamylopectin molecules such that the amylopectin molecules associate withone another via the polymers. The high molecular weight of the polymerenables it to simultaneously interact/entangle with several starchmolecules. That is, the high polymers function as molecular links forstarch molecules. The linking function of the high polymers isparticularly important for starches high in amylopectin content. Theentanglements and/or associations between starch and polymers enhancethe melt extensibility of the starch composition such that thecomposition is suitable for extensional processes. In one embodiment, itis found that the composition can be melt attenuated uniaxially to avery high draw ratio (greater than 1000).

[0034] In order to effectively form entanglements and/or associationswith the starch molecules, the high polymer suitable for use hereinshould have a weight-average molecular weight of at least 500,000.Typically the weight average molecular weight of the polymer ranges fromabout 500,000 to about 25,000,000, preferably from about 800,000 toabout 22,000,000, more preferably from about 1,000,000 to about20,000,000, and most preferably from about 2,000,000 to about15,000,000. The high molecular weight polymers are preferred due to theability to simultaneously interact with several starch molecules,thereby increasing extensional melt viscosity and reducing meltfracture.

[0035] Suitable high polymers have a δ_(Polymer) such that thedifference between δ_(starch) and δ_(polymer) is less than about 10MPa^(1/2), preferably less than about 5 MPa^(1/2), and more preferablyless than about 3 MPa^(1/2). Nonlimiting examples of suitable highpolymers include polyacrylamide and derivatives such as carboxylmodified polyacrylamide; acrylic polymers and copolymers includingpolyacrylic acid, polymethacrylic acid, and their partial esters; vinylpolymers including polyvinyl alcohol, polyvinylacetate,polyvinylpyrrolidone, polyethylene vinyl acetate, polyethyleneimine, andthe like; polyamides; polyalkylene oxides such as polyethylene oxide,polypropylene oxide, polyethylenepropylene oxide, and mixtures thereof.Copolymers made from mixtures of monomers selected from any of theaforementioned polymers are also suitable herein. Other exemplary highpolymers include water soluble polysaccharides such as alginates,carrageenans, pectin and derivatives, chitin and derivatives, and thelike; gums such as guar gum, xanthum gum, agar, gum arabic, karaya gum,tragacanth gum, locust bean gum, and like gums; water solublederivatives of cellulose, such as alkylcellulose, hydroxyalkylcellulose,carboxyalkylcellulose, and the like; and mixtures thereof.

[0036] Some polymers (e.g., polyacrylic acid, polymethacrylic acid) aregenerally not available in the high molecular weight range (i.e.,500,000 or higher). A small amount of crosslinking agents may be addedto create branched polymers of suitably high molecular weight usefulherein.

[0037] The high polymer is added to the composition of the presentinvention in an amount effective to visibly reduce the melt fracture andcapillary breakage of fibers during the spinning process such thatsubstantially continuous fibers having relatively consistent diametercan be melt spun. These polymers are typically present in the range fromabout 0.001 to about 10 wt %, preferably from about 0.005 to about 5 wt%, more preferably from about 0.01 to about 1 wt %, and most preferablyfrom about 0.05 to about 0.5 wt % of the composition. It is surprisingto find that at a relatively low concentration, these polymerssignificantly improve the melt extensibility of the starch composition.

[0038] The starch compositions may optionally include additives toenhance melt flow and melt processability, particularly theextensibility of the composition under the melt processing conditions.The additives may function as plasticizers and/or diluents to reduce themelt shear viscosity of the starch composition. The plasticizers areadded to the composition of the present invention in an amount effectiveto improve the flow, hence, the melt processability. The plasticizersmay also improve the flexibility of the final products, which isbelieved to be due to the lowering of the glass transition temperatureof the composition by the plasticizer. The plasticizers shouldpreferably be substantially compatible with the polymeric components ofthe present invention so that the plasticizers may effectively modifythe properties of the composition. As used herein, the term“substantially compatible” means when heated to a temperature above thesoftening and/or the melting temperature of the composition, theplasticizer is capable of forming a substantially homogeneous mixturewith starch (i.e., the composition appears transparent or translucent tothe naked eye).

[0039] Suitable for use herein as hydroxyl plasticizers are organiccompounds having at least one hydroxyl group, preferably a polyol.Without being bound by theory, it is believed that the hydroxyl groupsof the plasticizers enhance compatibility by forming hydrogen bonds withthe starch matrix material. Nonlimiting examples of useful hydroxylplasticizers include sugars such as glucose, sucrose, fructose,raffinose, maltodextrose, galactose, xylose, maltose, lactose, mannose,erythrose, glycerol, and pentaerythritol; sugar alcohols such aserythritol, xylitol, maltitol, mannitol and sorbitol; polyols such asethylene glycol, propylene glycol, dipropylene glycol, butylene glycol,hexane triol, and the like, and polymers thereof; and mixtures thereof.

[0040] Also useful herein as hydroxyl plasticizers are poloxomers(polyoxyethylene/polyoxypropylene block copolymers) and poloxamines(polyoxyethylene/polyoxypropylene block copolymers of ethylene diamine).Suitable “poloxomers” comprise block copolymers ofpolyoxyethylene/polyoxypropylene having the following structure:

HO—(CH₂—CH₂—O)_(x)—(CHCH₃—CH₂—O)_(y)—(CH₂—CH₂—O)_(z)—OH

[0041] wherein x has a value ranging from about 2 to about 40, y has avalue ranging from about 10 to about 50, and z has a value ranging fromabout 2 to about 40, and preferably x and z have the same value. Thesecopolymers are available as Pluronic® from BASF Corp., Parsippany, N.J.Suitable poloxamers and poloxamines are available as Synperonic® fromICI Chemicals, Wilmington, Del., or as Tetronic® from BASF Corp.,Parsippany, N.J.

[0042] Also suitable for use herein as hydroxyl-free plasticizers areother hydrogen bond forming organic compounds which do not have hydroxylgroup, including urea and urea derivatives; anhydrides of sugar alcoholssuch as sorbitan; animal proteins such as gelatin; vegetable proteinssuch as sunflower protein, soybean protein, and cotton seed protein; andmixtures thereof. All of the plasticizers may be used alone or inmixtures thereof.

[0043] Typically, the hydroxyl plasticizer comprises from about 1 wt %to about 70 wt %, more preferably from about 2 wt % to about 60 wt %,most preferably from about 3 wt % to about 40 wt % of the starchcomposition. The hydroxyl-free plasticizer typically comprises fromabout 0.1 wt % to about 70 wt %, preferably from about 2 wt % to about50 wt %, more preferably from about 3 wt % to about 40 wt % of thestarch composition.

[0044] In one embodiment, a mixture of the hydroxyl and hydroxyl-freeplasticizers is used, wherein the hydroxyl plasticizers are sugars, suchas sucrose, fructose, and sorbitol, and the hydroxyl-free plasticizersare urea and urea derivatives. It is found that urea and its derivativesin the starch composition of the present invention have a strongtendency to crystallize, that is, crystallization of urea and itsderivatives occurs even under fast cooling condition such as meltblowing, spun bonding, melt extrusion, wet spinning, and the like.Therefore, urea and urea derivatives may be used as solidifying agentsfor modifying or controlling the solidification rate of the starchcomposition of the present invention. In a preferred embodiment, amixture of sucrose and urea is added to the starch/polymer compositionin an amount effective to achieve the desired melt processability andsolidification rate.

[0045] Diluents such as polar solvents may be added to the starchcompositions of the present invention to adjust the melt shear viscosityand enhance the melt spinnability of the starch compositions. Generally,the melt shear viscosity decreases in a nonlinear manner as the diluentcontent is increased. Typically, the diluent is added in an amount fromabout 5 wt % to about 60 wt %, preferably from about 7 wt % to about 50wt %, more preferably from about 10 wt % to about 30 wt %, of the totalcomposition.

[0046] Suitable for use herein as diluents are polar solvents having asolubility parameter δ ranging from about 19 to about 48 MPa^(1/2),preferably from about 24 to about 48 MPa^(1/2), and more preferably fromabout 28 to about 48 MPa^(1/2). Nonlimiting examples include water,C1-C18 linear or branched alcohols, DMSO (dimethyl sulphoxide),formamide and derivatives such as N-methyl formamide, N-ethyl formamide,acetamide and derivatives such as methyl acetamide, Cellosolv® (a glycolalkyl ether) and derivatives, such as butyl Cellosolv®, benzylCellosolv®, Cellosolv® acetate (all Cellosolv® and derivatives areavailable from J.T. Baker, Phillipsburg, N.J.), hydrazine, and ammonia.It is also known that the δ value of a solvent mixture can be determinedby volume-averaging the δ values of the individual solvents. Therefore,mixed solvents having δ values within the above-identified range (i.e.,from about 19 to about 48 MPa^(1/2)) are also suitable for use herein.For example, a mixed solvent of DMSO/water having a composition of 90/10v/v would have a δ value of about 31.5; such a mixed solvent system issuitable for use herein.

[0047] It is found that polar solvents capable of forming hydrogenbonding are more effective in lowering the melt viscosity of thecomposition. As such, a lower amount of the polar solvent is sufficientto adjust the viscosity to the desired range for melt spinning. Using alower amount of the polar solvent provides a further advantage ofreducing the need for an evaporation step during or subsequent to themelt processing step, which results in operating cost advantages such aslower energy consumption and lower solvent recovery costs, as well aslower costs for environmental/regulatory compliance.

[0048] The starch composition may optionally include liquid or volatileprocessing aids which function mainly as viscosity modifiers of the meltcompositions. The processing aid is substantially volatized and removedduring the melt processing stage such that only a residual/trace amountremains in the final product. Thus, they do not adversely affect thestrength, modulus or other properties of the final product. The polarsolvents disclosed above may also function as volatile processing aids.Other nonlimiting examples include carbonates such as sodiumbicarbonate.

[0049] Optionally, other ingredients may be incorporated into thespinnable starch composition to modify the processability and/or tomodify physical properties such as elasticity, tensile strength andmodulus of the final product. Nonlimiting examples include oxidationagents, cross-linking agents, emulsifiers, surfactants, debondingagents, lubricants, other processing aids, optical brighteners,antioxidants, flame retardants, dyes, pigments, fillers, proteins andtheir alkali salts, biodegradable synthetic polymers, waxes, low meltingsynthetic thermoplastic polymers, tackifying resins, extenders, wetstrength resins and mixtures thereof. These optional ingredients may bepresent in quantities ranging from about 0.1% to about 70%, preferablyfrom about 1% to about 60%, more preferably from about 5% to about 50%,and most preferably from about 10% to about 50%, by weight of thecomposition.

[0050] Exemplary biodegradable synthetic polymers includepolycaprolactone; polyhydroxyalkanoates including polyhydroxybutyrates,and polyhydroxyvalerates; polylactides; and mixtures thereof.

[0051] Lubricant compounds may further be added to improve the flowproperties of the starch material during the processes used forproducing the present invention. The lubricant compounds can includeanimal or vegetable fats, preferably in their hydrogenated form,especially those which are solid at room temperature. Additionallubricant materials include mono-glycerides and di-glycerides andphosphatides, especially lecithin. For the present invention, apreferred lubricant compound includes the mono-glyceride, glycerolmono-stearate.

[0052] Further additives including inorganic particles such as theoxides of magnesium, aluminum, silicon, and titanium may be added asinexpensive fillers or extenders. Additionally, additives such asinorganic salts, including alkali metal salts, alkaline earth metalsalts, phosphate salts, etc., may be used.

[0053] Other additives may be desirable depending upon the particularend use of the product contemplated. For example, in products such astoilet tissue, disposable towels, facial tissues and other similarproducts, wet strength is a desirable attribute. Thus, it is oftendesirable to add to the starch polymer cross-linking agents known in theart as “wet strength” resins.

[0054] A general dissertation on the types of wet strength resinsutilized in the paper art can be found in TAPPI monograph series No. 29,Wet Strength in Paper and Paperboard, Technical Association of the Pulpand Paper Industry (New York, 1965). The most useful wet strength resinshave generally been cationic in character. Polyamide-epichlorohydrinresins are cationic polyamide amine-epichlorohydrin wet strength resinswhich have been found to be of particular utility. Suitable types ofsuch resins are described in U.S. Pat. No. 3,700,623, issued on Oct. 24,1972, and U.S. Pat. No. 3,772,076, issued on Nov. 13, 1973, both issuedto Keim and both being hereby incorporated by reference. One commercialsource of a useful polyamide-epichlorohydrin resin is Hercules, Inc. ofWilmington, Del., which markets such resins under the mark Kymene®.

[0055] Glyoxylated polyacrylamide resins have also been found to be ofutility as wet strength resins. These resins are described in U.S. Pat.No. 3,556,932, issued on Jan. 19, 1971, to Coscia, et al. and U.S. Pat.No. 3,556,933, issued on Jan. 19, 1971, to Williams et al., both patentsbeing incorporated herein by reference. One commercial source ofglyoxylated polyacrylamide resins is Cytec Co. of Stanford, Conn. whichmarkets one such resin under the mark Parez® 631NC.

[0056] It is found that when suitable cross-linking agent such as Parez®631NC is added to the starch composition of the present invention underacidic condition. The composition is rendered water insoluble. That is,the water solubility of the composition, as tested by the Test Methoddescribed hereinafter, is less than 30%, preferably less than 20%, morepreferably less than 10% and most preferably less than 5%. The productssuch as fibers and films made from such a composition are also waterinsoluble.

[0057] Still other water-soluble cationic resins finding utility in thisinvention are urea formaldehyde and melamine formaldehyde resins. Themore common functional groups of these polyfunctional resins arenitrogen containing groups such as amino groups and methylol groupsattached to nitrogen. Polyethylenimine type resins may also find utilityin the present invention. In addition, temporary wet strength resinssuch as Caldas® 10 (manufactured by Japan Carlit) and CoBond® 1000(manufactured by National Starch and Chemical Company) may be used inthe present invention.

[0058] For the present invention, a suitable cross-linking agent isadded to the composition in quantities ranging from about 0.1% by weightto about 10% by weight, more preferably from about 0.1% by weight toabout 3% by weight.

[0059] The Rheology of the Starch Compositions

[0060] The rheological behavior of the starch composition is animportant consideration for selecting suitable materials and fabricationequipment/processes. Many factors contribute to the rheological behaviorof the starch composition, including the amount and the type ofpolymeric components used, the molecular weight and molecular weightdistribution of the components, the amount and type of additives (e.g.,plasticizers, processing aids), the processing conditions such astemperature, pressure, rate of deformation, and relative humidity, andin the case of non-Newtonian materials, the deformation history (i.e., atime or strain history dependence).

[0061] The starch composition of the present invention typically has ahigh solid content (i.e., a concentration above a critical concentrationC*) such that a dynamic or fluctuating entangled network is formedwherein the starch molecules and the high polymers become associated anddisassociated temporally. The association may be in the form of physicalentanglements, van der Waals forces, or chemical interactions such ashydrogen bonding. The starch composition having the entangled networkstructure exhibits melt flow behavior typical of a non-Newtonian fluid.

[0062] The starch composition of the present invention may exhibit astrain hardening behavior, that is, the extensional viscosity increasesas the strain or deformation increases. Typically, a Newtonian fluidexhibit a linear relationship between stress/force and strain. That is,there is no strain hardening behavior in a Newtonian fluid. On the otherhand, a non-Newtonian fluid may exhibiting an increase in force athigher strain (i.e, strain hardening) while still exhibit a linearforce-strain relationship at lower strain (i.e, Newtonian-like).

[0063] The strain experienced by a fluid element in a non-Newtonianfluid is dependent on its kinematic history, that isɛ = ∫₀^(t)ɛ ⋅ (t^(′))∂t^(′)

[0064] This time or history dependent strain is called the Hencky strain(ε_(H)). For an ideal homogeneous uniaxial elongation, the strain rateexperienced by every fluid element is equal to the strain imposed by theapplied stress, such as the stresses applied externally by theinstrument, device or process. In such an ideal case, the Hencky straincorrelates directly with the sample deformation/elongation

ε_(H) =ln (L/L _(O))

[0065] Such an ideal strain response to applied stress is most oftenobserved in Newtonian fluids.

[0066] The Trouton ratio (Tr) is often used to express the extensionalflow behavior. The Trouton ratio is defined as the ratio between theextensional viscosity (η_(e)) and the shear viscosity (η_(s)),

Tr=η _(e)(ε·, t)/η_(s)

[0067] wherein the extensional viscosity η_(e) is dependent on thedeformation rate (ε^(·)) and time (t). For a Newtonian fluid, theuniaxial extension Trouton ratio has a constant value of 3. For anon-Newtonian fluid, the extensional viscosity is dependent on thedeformation rate (ε^(·)) and time (t).

[0068] Shear viscosity (η_(s)) relates to the melt processability of thestarch composition using standard polymer processing techniques, such asextrusion, blow molding, compression molding, injection molding and thelike. A starch composition having a shear viscosity, measured accordingto the Test Method disclosed hereinafter, of less than about 30 Pa·s,preferably from about 0.1 to about 10 Pa·s, more preferably from about 1to about 8 Pa·s, is useful in the melt attenuation processes herein.Some starch compositions herein may have low melt viscosity such thatthey may be mixed, conveyed, or otherwise processed in traditionalpolymer processing equipment typically used for viscous fluids, such asa stationary mixer equipped with metering pump and spinneret. The shearviscosity of the starch composition may be effectively modified by themolecular weight and molecular weight distribution of the starch, themolecular weight of the high polymer, and the amount of plasticizersand/or solvents used. It is found that reducing the average molecularweight of the starch is an effective way to lower the shear viscosity ofthe composition.

[0069] It is generally known that melt shear viscosity is a materialproperty useful for evaluating melt processability of the material intraditional thermoplastic processes such as injection molding orextrusion. For conventional fiber spinning thermoplastics such aspolyolefins, polyamides and polyesters, there is a strong correlationbetween shear viscosity and extensional viscosity of these conventionalthermoplastic materials and blends thereof. That is, the spinnability ofthe material can be determined simply by the melt shear viscosity, eventhough the spinnablity is a property controlled primarily by meltextensional viscosity. The correlation is quite robust such that thefiber industry has relied on the melt shear viscosity in selecting andformulating melt spinnable materials. The melt extensional viscosity hasrarely been used as an industrial screening tool.

[0070] It is therefore surprising to find that the starch compositionsof the present invention do not exhibit such a correlation between shearand extensional viscosities. Specifically, when a high polymer selectedaccording to the present invention is added to a starch composition, theshear viscosity of the composition remains relatively unchanged, or evendecreases slightly. Based on conventional wisdom, such a starchcomposition would exhibit decreased melt processability and would not besuitable for melt extensional processes. However, it is surprisinglyfound that the starch composition herein shows a significant increase inextensional viscosity when even a small amount of high polymer is added.Consequently, the starch composition herein is found to have enhancedmelt extensibility and is suitable for melt extensional processes (e.g.,blow molding, spun bonding, blown film molding, foam molding, and thelike).

[0071] Extensional or elongational viscosity (η_(e)) relates to meltextensibility of the composition, and is particularly important forextensional processes such as fiber, film or foam making. Theextensional viscosity includes three types of deformation: uniaxial orsimple extensional viscosity, biaxial extensional viscosity, and pureshear extensional viscosity. The uniaxial extensional viscosity isimportant for uniaxial extensional processes such as fiber spinning,melt blowing, and spun bonding. The other two extensional viscositiesare important for the biaxial extension or forming processes for makingfilms, foams, sheets or parts. It is found that the properties of thehigh polymers have a significant effect on melt extensional viscosity.The high polymers useful for enhancing the melt extensibility of thestarch composition of the present invention are typically high molecularweight, substantially linear polymers. Moreover, high polymers that aresubstantially compatible with starch are most effective in enhancing themelt extensibility of the starch composition.

[0072] It has been found that starch compositions useful for meltextensional processes typically hasve their extensional viscosityincreased by a factor of at least 10 when a selected high polymer isadded to the composition. Typically, the starch compositions of presentinvention show an increase in the extensional viscosity of about 10 toabout 500, preferably of about 20 to about 300, more preferably fromabout 30 to about 100, when a selected high polymer is added.

[0073] It has also been found that melt processable compositions of thepresent invention typically have a Trouton ratio of at least about 3.Typically, the Trouton ratio ranges from about 10 to about 5,000,preferably from about 20 to about 1,000, more preferably from about 30to about 500, when measured at 90° C. and 700 s⁻¹.

[0074] When the starch composition of the present composition issubjected to an uniaxial extensional process, a draw ratio, expressed in(D_(O) ²/D²) wherein D_(O) is the diameter of filament before drawingand D is the diameter of the drawn fiber, greater than 1000 can beeasily achieved. The starch composition of the present inventiontypically achieves a draw ratio from about 5 to about 6,000, preferablyfrom about 10 to about 3,000, more preferably from about 20 to about1,000 and most preferably from about 30 to about 500. More specifically,the starch composition of the present invention has sufficient meltextensibility to be melt drawn to fine fibers having a finite averagediameter of less than 50 microns, preferably less than 25 microns, morepreferably less than 15 microns, even more preferably less than 10microns, and most preferably less than 5 microns.

[0075] When the starch composition of the present invention is subjectedto a biaxial extensional process, the enhanced melt extensibility of thecomposition allows it to be melt drawn to films having a finite averagecaliper of less than 0.8 mils, preferably less than 0.6 mils, morepreferably less than 0.4 mils, even more preferably less than 0.2 mils,and most preferably less than 0.1 mils.

[0076] The starch composition herein is processed in a flowable state,which typically occurs at a temperature at least equal to or higher thanits melting temperature. Therefore, the processing temperature range iscontrolled by the melting temperature of the starch composition, whichis measured according to the Test Method described in detail herein. Themelting temperature of the starch composition herein ranges from about80 to 180° C., preferably from about 85 to about 160° C., and morepreferably from about 90 to about 140° C. It is to be understood thatsome starch compositions may not exhibit pure “melting” behavior. Asused herein, the term “melting temperature” means the temperature or therange of temperature at or above which the composition melts or softens.

[0077] Exemplary uniaxial extensional processes suitable for the starchcompositions include melt spinning, melt blowing, and spun bonding.These processes are described in detail in U.S. Pat. No. 4,064,605,issued on Dec. 27, 1977 to Akiyama et al.; U.S. Pat. No. 4,418,026,issued on Nov. 29, 1983 to Blackie et al.; U.S. Pat. No. 4,855,179,issued on Aug. 8, 1989 to Bourland et al.; U.S. Pat. No. 4,909,976,issued on Mar. 20, 1990 to Cuculo et al.; U.S. Pat. No. 5,145,631,issued on Sep. 8, 1992 to Jezic; U.S. Pat. No. 5,516,815, issued on May14, 1996 to Buehler et al.; and U.S. Pat. No. 5,342,335, issued on Aug.30, 1994 to Rhim et al.; the disclosure of all of the above areincorporated herein by reference. The resultant products may find use infilters for air, oil and water; vacuum cleaner filters; furnace filters;face masks; coffee filters, tea or coffee bags; thermal insulationmaterials and sound insulation materials; nonwovens for one-time usesanitary products such as diapers, feminine pads, and incontinencearticles; biodegradable textile fabrics for improved moisture absorptionand softness of wear such as microfiber or breathable fabrics; anelectrostatically charged, structured web for collecting and removingdust; reinforcements and webs for hard grades of paper, such as wrappingpaper, writing paper, newsprint, corrugated paper board, and webs fortissue grades of paper such as toilet paper, paper towel, napkins andfacial tissue; medical uses such as surgical drapes, wound dressing,bandages, dermal patches and self-dissolving sutures; and dental usessuch as dental floss and toothbrush bristles. The fibrous web may alsoinclude odor absorbants, termite repellants, insecticides, rodenticides,and the like, for specific uses. The resultant product absorbs water andoil and may find use in oil or water spill clean-up, or controlled waterretention and release for agricultural or horticultural applications.The resultant starch fibers or fiber webs may also be incorporated intoother materials such as saw dust, wood pulp, plastics, and concrete, toform composite materials, which can be used as building materials suchas walls, support beams, pressed boards, dry walls and backings, andceiling tiles; other medical uses such as casts, splints, and tonguedepressors; and in fireplace logs for decorative and/or burning purpose.

[0078] The melt theological behavior of the present starch compositionalso makes it suitable for use in conventional thermoplastic processesthat involves biaxial extension of the material. By having the propermelt shear viscosity and biaxial extensional viscosity, the starchcompositions of the present invention may substantially reduce theoccurrence of tearing, surface defects, and other breakdowns or defectsthat interrupt continuous processes and produce unsatisfactory products.These processes include blow molding, blown film extrusion orcoextrusion, vacuum forming, pressure forming, compression molding,transfer molding and injection molding. Nonlimiting examples of theseprocesses are described in details in U.S. Pat. No. 5,405,564,issued onApr. 11, 1995 to Stepto et al.; U.S. Pat. No. 5,468,444, issued on Nov.21, 1995 to Yazaki et al.; U.S. Pat. No. 5,462,982, issued on Oct. 31,1995 to Bastioli et al.; the disclosure of all of the above are herebyincorporated by reference. The articles produced by these processesinclude sheets, films, coatings, laminates, pipes, rods, bags, andshaped articles (such as bottles, containers). The articles may find useas bags such as shopping bags, grocery bags, and garbage bags; pouchesfor food storage or cooking; microwavable containers for frozen food;and pharmaceutical uses such as capsules or coatings for medicine. Thefilms may be substantially transparent for use as food wraps, shrinkwraps or windowed envelopes. The films may also be further processed foruse as an inexpensive, biodegradable carrier for other materials such asseeds or fertilizers. Adhesives may be applied to the films or sheetsfor other uses such as labels.

[0079] The starch compositions of the present invention may also be madeinto a foamed structure by controlled removal of the volatile components(e.g., water, polar solvents). However, foaming or expanding agents aregenerally incorporated to produce articles having foamed or porousinternal structure. Exemplary foaming or expanding agents include carbondioxide, n-pentane, and carbonate salts such as sodium bicarbonate,either alone or in combination with a polymeric acid which has lateralcarboxyl groups (e.g., polyacrylic acid, ethylene-acrylic copolymer).Nonlimiting examples of the foaming and forming processes are describedin U.S. Pat. No. 5,288,765, issued on Feb. 22, 1994 to Bastioli et al.;U.S. Pat. No. 5,496,895, issued on Mar. 5, 1996 to Chinnaswamy et al.;U.S. Pat. No. 5,705,536, issued on Jan. 6, 1998 to Tomka; and U.S. Pat.No. 5,736,586, issued on Apr. 7, 1998 to Bastioli et al.; thedisclosures of which are hereby incorporated by reference. The resultantproducts may find use in egg cartons; foamed cups for hot beverages;containers for fast food; meat trays; plates and bowls for one-time usesuch as at picnic or parties; packaging materials, either loose-fill ormolded to conform to the packed article (e.g., a computer shippingpackage); thermal insulation materials; and noise insulation or soundproofing materials.

[0080] Test Methods

[0081] A. Shear Viscosity

[0082] The shear viscosity of the composition is measured using arotational viscometer (Model DSR 500, manufactured by Rheometrics). Apreheated sample composition is loaded into the barrel section of therheometer, and substantially fills the barrel section (about 60 grams ofsample is used). The barrel is held at a test temperature of 90° C.After the loading, air generally bubbles to the surface and does createproblems for the run. For a more viscous samples, compaction prior torunning the test may be used to rid the molten sample of entrapped air.The viscometer is programmed to ramp the applied stress from 10 dyne/cmto 5000 dyne/cm. The strain experienced by the sample is measure by astrain gauge. The apparent viscosity of the composition can be derivedtherefrom. Then log (apparent shear viscosity) is plotted against log(shear rate) and the plot is fitted by the power law η=K γ^(n−1),wherein K is a material constant, γ is the shear rate. The reportedshear viscosity of the starch composition herein is an extrapolation toa shear rate of 700 s⁻¹ using the power law relation.

[0083] B. Extensional Viscosity

[0084] The extensional viscosity is measured using a capillary rheometer(Model Rheograph 2003, manufactured by Geottfert). The measurements areconducted using an orifice die having a diameter D of 0.5 mm and alength L of 0.25 mm (i.e., L/D=0.5). The die is attached to the lowerend of a barrel, which is held at a test temperature of 90° C. Apreheated sample composition is loaded into the barrel section of therheometer, and substantially fills the barrel section. After theloading, air generally bubbles to the surface and does create problemsfor the run. For more viscous compositions, compaction prior to runningthe test may be used to rid the molten sample of entrapped air. A pistonis programmed to push the sample from the barrel through the orifice dieat a chosen rate. As the sample goes from the barrel through the orificedie, the sample experiences a pressure drop. An apparent viscosity canbe obtained from the pressure drop and the flow rate of the samplethrough the orifice die. Corrections are often applied to the apparentviscosity following procedures generally known in the art. A shearcorrection factor and Cogswell equation are applied to the calculationof the extensional viscosity. The corrected extensional viscosity at 700s⁻¹ is reported.

[0085] It is known that the extensional viscosity can be measured usingan orifice die and applying the correction factors, following the methoddescribed herein. More details of extensional viscosity measurements aredisclosed in S. H. Spielberg et al., The Role Of End-Effects OnMeasurements Of Extensional Viscoistv In Filament Stretching Rheometers,Journal of Non-Newtonian Fluid Mechanics, Vol. 64, 1996, p. 229-267;Bhattacharya, et al., Uniaxial Extensional Viscoisty During ExtrusionCooking From Entrance Pressure Drop Method, Journal of Food Science,Vol. 59, No. 1, 1994, p. 221-226; both are hereby incorporated byreference. It is also known that the extensional viscosity can bemeasured using a hyperbolic or semi-hyperbolic die. Detailed disclosureof extensional viscosity measurements using a semi-hyperbolic die isdisclosed in U.S. Pat. No. 5,357,784, issued Oct. 25, 1994 to Collier,the disclosure of which is incorporated herein by reference.

[0086] C. Molecular Weight and Molecular Weight Distribution

[0087] The weight-average molecular weight (Mw) and molecular weightdistribution (MWD) of starch are determined by Gel PermeationChromatography (GPC) using a mixed bed column. Parts of the instrumentare as follows: Pump Waters Model 600E System controller Waters Model600E Autosampler Waters Model 717 Plus Column PL gel 20 μm Mixed Acolumn (gel molecular weight ranges from 1,000 to 40,000,000) having alength of 600 mm and an internal diameter of 7.5 mm. Detector WatersModel 410 Differential Refractometer GPC software Waters Millenium ®software

[0088] The column is calibrated with Dextran standards having molecularweights of 245,000; 350,000; 480,000; 805,000; and 2,285,000. TheseDextran calibration standards are available from American PolymerStandards Corp., Mentor, Ohio. The calibration standards are prepared bydissolving the standards in the mobile phase to make a solution of about2 mg/ml. The solution sits undisturbed overnight. Then it is gentlyswirled and filtered through a syringe filter (5 μm Nylon membrane,Spartan-25, available from VWR) using a syringe (5 ml, Norm-Ject,available from VWR).

[0089] The starch sample is prepared by first making a mixture of 40 wt% starch in tap water, with heat applied until the mixture gelatinizes.Then 1.55 grams of the gelatinized mixture is added to 22 grams ofmobile phase to make a 3 mg/ml solution which is prepared by stirringfor 5 minutes, placing the mixture in an oven at 105° C. for one hour,removing the mixture from the oven, and cooling to room temperature. Thesolution is filtered using the syringe and syringe filter as describedabove.

[0090] The filtered standard or sample solution is taken up by theautosampler to flush out previous test materials in a 100 μl injectionloop and inject the present test material into the column. The column isheld at 70° C. The sample eluded from the column is measured against themobile phase background by a differential refractive index detector heldat 50° C. and with the sensitivity range set at 64. The mobile phase isDMSO with 0.1% w/v LiBr dissolved therein. The flow rate is set at 1.0ml/min and in the isocratic mode (i.e., the mobile phase is constantduring the run). Each standard or sample is run through the GPC threetimes and the results are averaged.

[0091] The average molecular weight of the high polymer is provided bythe material suppliers.

[0092] D. Thermal Properties

[0093] Thermal properties of the present starch compositions aredetermined using a TA Instruments DSC-2910 which has been calibratedwith an indium metal standard, which has an melting temperature (onset)of 156.6° C. and a heat of melting of 6.80 calories per gram, asreported in the chemical literature. Standard DSC operating procedureper manufacturer's Operating Manual is used. Due to the volatileevolution (e.g., water vapor) from the starch composition during a DSCmeasurement, a high volume pan equipped with an o-ring seal is used toprevent the escape of volatiles from the sample pan. The sample and aninert reference (typically an empty pan) are heated at the same rate ina controlled environment. When an actual or pseudo phase change occursin the sample, the DSC instrument measures the heat flow to or from thesample versus that of the inert reference. The instrument is interfacedwith a computer for controlling the test parameters (e.g., theheating/cooling rate), and for collecting, calculating and reporting thedata.

[0094] The sample is weighed into a pan and enclosed with an o-ring anda cap. A typical sample size is 25-65 milligrams. The enclosed pan isplaced in the instrument and the computer is programmed for the thermalmeasurement as follows:

[0095] 1. equilibrate at 0° C.;

[0096] 2. hold for 2 minutes at 0° C.;

[0097] 3. heat at 10° C./min to 120° C.;

[0098] 4. hold for 2 minutes at 120° C.;

[0099] 5. cool at 10° C./min to 30° C.;

[0100] 6. equilibrate at ambient temperature for 24 hours, the samplepan may be removed from the DSC instrument and placed in a controlledenvironment at 30° C. in this duration;

[0101] 7. return sample pan to the DSC instrument and equilibrate at 0°C.;

[0102] 8. hold for 2 minutes;

[0103] 9. heat at 10° C./min to 120° C.;

[0104] 10. hold for 2 minutes at 120° C.;

[0105] 11. cool at 10° C./min to 30° C. and equilibrate; and

[0106] 12. remove the used sample.

[0107] The computer calculates and reports the thermal analysis resultas differential heat flow (ΔH) versus temperature or time. Typically thedifferential heat flow is normalized and reported on per weight basis(i.e, cal/mg). Where the sample exhibits a pseudo phase transition, suchas a glass transition, a differential of the ΔH v. time/temperature plotmay be employed to more easily determine a glass transition temperature.

[0108] E. Water Solubility

[0109] A sample composition is made by mixing the components with heatand stirring until a substantially homogeneous mixture is formed. Themelt composition is cast into a thin film by spreading it over a Teflon®sheet and cooling at ambient temperature. The film is then driedcompletely (i.e., no water in the film/composition) in an oven at 100°C. The dried film is then equilibrated to room temperature. Theequilibrated film is ground into small pellets.

[0110] To determine the % solids in the sample, 2 to 4 grams of theground sample is placed in a pre-weighed metal pan and the total weightof pan and sample is recorded. The weighed pan and sample is placed in a100° C. oven for 2 hours., and then taken out and weighed immediately.The % solids is calculated as follows:${\% \quad {Solids}} = {\frac{\left( {{{{{dried}\quad {weight}\quad {of}\quad {ground}\quad {sample}}\&}\quad {pan}} - {{weight}\quad {of}\quad {pan}}} \right)}{\left( {{{{{first}\quad {weight}\quad {of}\quad {ground}\quad {sample}}\&}\quad {pan}} - {{weight}\quad {of}\quad {pan}}} \right)} \times 100}$

[0111] To determine the solubility of the sample composition, weigh 10grams of ground sample in a 250 mL beaker. Add deionized water to make atotal weight of 100 grams. Mix the sample and water on a stir plate for5 minutes. After stirring, pour at least 2 mL of stirred sample into acentrifuge tube. Centrifuge 1 hour at 20,000 g at 10° C. Take thesupernatant of the centrifuged sample and read the refractive index. The% solubility of the sample is calculated as follows:${\% \quad {Soluble}\quad {Solids}} = \frac{\left( {{Refractive}\quad {Index}\quad \#} \right) \times 1000}{\% \quad {Solids}}$

[0112] F. Caliper

[0113] Prior to testing, the film sample is conditioned at a relativehumidity of 48%-50% and at a temperature of 22° C. to 24° C. until amoisture content of about 5% to about 16% is achieved. The moisturecontent is determined by TGA (Thermo Gravimetric Analysis). For ThermalGravimetric Analysis, a high resolution TGA2950 Termogravimetricanalyzer from TA Instruments is used. Approximately 20 mg of sample isweighed into a TGA pan. Following the manufacturer's instructions, thesample and pan are inserted into the unit and the temperature isincreased at a rate of 10° C./minute to 250° C. The % moisture in thesample is determined using the weight lost and the initial weight asfollows:${\% \quad {Moisture}} = {\frac{{{Start}\quad {Weight}} - {{{Weight}@250^{{^\circ}}}\quad {C.}}}{{Start}\quad {Weight}}*100\%}$

[0114] Preconditioned samples are cut to a size greater than the size ofthe foot used to measure the caliper. The foot to be used is a circlewith an area of 3.14 square inches.

[0115] The sample is placed on a horizontal flat surface and confinedbetween the flat surface and a load foot having a horizontal loadingsurface, where the load foot loading surface has a circular surface areaof about 3.14 square inches and applies a confining pressure of about 15g/square cm (0.21 psi) to the sample. The caliper is the resulting gapbetween the flat surface and the load foot loading surface. Suchmeasurements can be obtained on a VIR Electronic Thickness Tester ModelII available from Thwing-Albert, Philadelphia, Pa. The calipermeasurement is repeated and recorded at least five times. The result isreported in mils.

[0116] The sum of the readings recorded from the caliper tests isdivided by the number of readings recorded. The result is reported inmils.

EXAMPLES

[0117] The materials used in the Examples are as follows:

[0118] Crystal Gum® is a modified starch having a weight-averagemolecular weight of 100,000; Nadex® is a modified starch having a weightaverage molecular weight of 2,000; and Instant-n Oil® is a modifiedstarch having a weight average molecular weight of 800,000; all areavailable from National Starch and Chemicals Corp., Bridgewater, N.J.

[0119] Superfloc® A-130 is a carboxylated polyacrylamide having aweight-average molecular weight of 12,000,000 to 14,000,000 and isavailable from Cytec Co., Stamford, Conn.

[0120] Nonionic polyacrylamides PAM-a and PAM-b having a weight-averagemolecular weight of 15,000,000, and 5,000,000 to 6,000,000,respectively, are available from Scientific Polymer Products, Inc.,Ontario, N.Y.

[0121] Polyethyleneimine having a weight-average molecular weight of750,000 is available from Aldrich Chemical Co., Milwaukee, Wis.

[0122] Parez® 631 NC is a low molecular weight glyoxylatedpolyacrylamide, and Parez® 802 is a low molecular weight glyoxylatedurea resin, both are available from Cytec Co., Stamford, Conn.

[0123] Pluronic® F87 is nonionic poloxomer, available form BASF corp.,Parsippany, N.J.

[0124] Urea, sucrose and glyoxal (in 40% solution in water) areavailable from Aldrich Chemical Co., Milwaukee, Wis.

Example 1

[0125] A melt processable composition of the invention is prepared bymixing 45 wt % starch (Crystal Gum), 40.5 wt % urea, 4.5 wt % sucrose,and 9.8 wt % free water, and manually stirring to form a slurry.Polyacrylamide (PAM-a, Mw=15,000,000) is dissolved in water to form aPAM aqueous solution. An aliquot of the polymer/water solution is addedto the slurry. Water in the slurry is then evaporated until the weightpercent of polyacrylamide in the final mixture is 0.2 wt %.

[0126] The composition has a shear viscosity of 0.65 Pa·s and anextensional viscosity of 1863.2 Pa·s, at 700s⁻¹ and 90° C.

Comparative Example 1b

[0127] A comparative starch composition is prepared according to Example1 except no polyacrylamide is added to the composition. The compositionhas a shear viscosity of 1.35 Pa·s and an extensional viscosity of 43.02Pa·s, at 700s⁻¹and 90° C. Example 1 and Comparative Example 1bdemonstrate that addition of a small amount of high polymer decreasesthe shear viscosity slightly and significantly increases the extensionalviscosity.

Example 2

[0128] A melt processable composition of the invention is prepared bymixing 50wt % starch (Crystal Gum), 30 wt % urea, 1.5 wt % sucrose, and18.5 wt % free water, and manually stirring to form a slurry.Polyacrylamide (Superfloc A-130, Mw=12-14,000,000) is dissolved in waterto form a PAM aqueous solution. An aliquot of the polymer/water solutionis added to the slurry. Water in the slurry is then evaporated until theweight percent of polyacrylamide in the final mixture is 0.003 wt %.

[0129] The composition has a shear viscosity of 1.12 Pa·s and anextensional viscosity of 46.0 Pa·s, at 700s⁻¹ and 90° C.

Comparative Example 2b

[0130] A comparative starch composition is prepared according to Example2 except no polyacrylamide is added to the composition. The compositionhas a shear viscosity of 1.23 Pa·s and an extensional viscosity of 0.69Pa·s, at 700s⁻¹ and 90° C. Example 2 and Comparative Example 2bdemonstrate that addition of a small amount of high polymer decreasesthe shear viscosity slightly and significantly increases the extensionalviscosity.

Example 3

[0131] A torque rheometer having a melt blowing die is used to processthe composition of Example 1. The torque rheometer is illustrated inFIG. 1. The torque rheometer assembly 100 includes a drive unit 110(Model Rheocord 90 available from Haake GmbH), a barrel 120 partitionedinto four temperature zones 122, 124, 126 and 128, a feed port 121, anda melt spinning die assembly 130. Twin screw elements 160 (model TW100,from Haake GmbH) are attached to the drive unit 110 and disposed withinthe barrel 120. A six inch wide melt blowing die assembly 130 (availablefrom JM Laboratories, Dawsonville, Ga.) is connected to the end of thebarrel via a pump 140. The die assembly has a spinneret plate which has52 holes per linear inch and a hole diameter of 0.015″ (0.0381 cm),surrounded by a 0.02″ wide air passageway 152, from which a highvelocity air stream 150 impinges the extruded filaments just below thespinneret plate. The air stream has the effect of simultaneously blowingthe filaments away from the spinneret and attenuating the filaments.

[0132] The composition of is prepared (as described in Example 1) bymixing 45 wt % starch (Crystal Gum), 0.2 wt % polyacrylamide (PAM-a),40.5 wt % urea, 4.5 wt % sucrose, and 9.8 wt % water. The mixture isgravity-fed via feed port 121 into a torque rheometer. The torquerheometer and die assembly are set as follows: Barrel Temperature Zone122   70° C. Zone 124   90° C. Zone 126   90° C. Zone 128   90° C.Torque 100 rpm Die Temperature 126.7° C. Air Temperature 126.7° C. AirPressure 35 psi Pump  40 rpm

[0133] The mixture is conveyed from the extruder through the pump intothe melt blowing die. The resulting attenuated filaments (or finefibers) of the invention have fiber diameters ranging from 8 to 40microns.

[0134] Note that the weight percent starch in the melt processablecomposition includes the weight of starch and the weight of bound water(which is on the average about 8 wt % of the starch). It is to beunderstood that the as-prepared compositions are used for uniaxial andbiaxial extensional processes. However, most of the water is lost duringthe melt process, and the resulting starch fiber, film or like productcontains little or no free water. The resulting product does containsome bound water (possible by absorbing moisture from ambientenvironment). Therefore, the composition of the resulting product may bemore appropriately expressed by its solid components, calculated on adry solid basis. For example, to calculate, on a dry solid basis, thecomposition of the fiber made according to Example 3, one would take outthe 9.8 wt % free water from the overall composition and the 8 wt %bound water from the starch, then normalize the remaining solid contentto 100%. Thus, the composition of the fiber of Example 3 calculated on adry solid basis would be 47.8 wt % starch solid (without bound water),0.23 wt % polyacrylamide, 46.8 wt % urea and 5.2 wt % sucrose.

Example 4

[0135] The composition of Example 2 is melt blown into fine fibers ofthe invention. FIG. 3a is the Scanning Electron Micrographs of finestarch fibers made from the composition of Example 2 using the processdescribed in Example 3, shown on a 200 micron scale. FIG. 3b is theScanning Electron Micrographs of the same starch fibers shown on a 20micron scale. Both figures show that starch fibers of Example 4 have afairly consistent fiber diameter of about 5 microns.

Example 5

[0136] Fifteen grams of starch (Crystal Gum, Mw=100,000 ) and fifteengrams of free water are mixed together at 80° C. with manual stirringuntil the mixture becomes substantially homogeneous or gelatinizes. Ahigh polymer (PAM-a, Mw=15,000,000) is dissolved in free water to form aPAM aqueous solution of known concentration. An aliquot of thepolymer/water solution is added to the starch/water mixture such thatthe overall mixture contains 0.006 grams of PAM-a. Then the overallmixture is heated to evaporate water until the weight of the finalmixture (starch, PAM-a and water) equals 30 grams. This mixture issubjectively shown to have suitable melt extensibility for drawingfibers.

Examples 6-8

[0137] Mixtures of starch (Crystal Gum), high polymer and water areprepared in the same manner as in Example 5. The final compositions ofthese mixture are shown below. Mw Ex-6 Ex-7 Ex-8 Starch Crystal 100,000wt % 49.99 49.99 46.92 Gum Polyacrylamide Superfloc 12-14,000,000 wt %0.02 A-130 PAM-b  5-6,000,000 wt % 0.02 Poly- 750,000 wt % 6.17ethyleneimine Water wt % 49.99 49.99 46.91

[0138] These compositions of the invention are subjectively shown tohave suitable melt extensibility for drawing fibers.

Examples 9-11

[0139] The following compositions are prepared in the same manner asExample 1. Mw Ex-9 Ex-10 Ex-11 Starch Crystal   100,000 wt % 41.54 20.7720.77 Gum Nadex    2,000 wt % 20.77 Instant-   800,000 wt % 20.77 n OilPolyacrylamide PAM-a 15,000,000 wt % 0.08 0.08 0.08 Urea wt % 6.23 6.236.23 Sucrose wt % 6.23 6.23 6.23 Parez 631 NC wt % 1.04 1.04 1.04 Waterwt % 44.88 44.88 44.88

[0140] These compositions of the invention are expected to have suitablemelt extensibility for drawing fibers. And where the water has beenadjusted to about pH 2, the resulting fibers are expected to have awater solubility of less than 30%, based on the test method disclosedherein.

Example 12

[0141] A melt processable composition is prepared by mixing 45 wt %starch (Crystal Gum), 0.2 wt % polyacrylamide (PAM-a), 40.5 wt % urea,4.5 wt % sucrose, and 9.8 wt % water to form a slurry. The compositionis melt blown into fine fibers using a torque rheometer as shown in FIG.1 in the manner described in Example 3, except the mixture is meter-fedinto the torque rheometer. The torque rheometer and die assembly are setas follows: Barrel Temperature Zone 122   70° C. Zone 124   90° C. Zone126   90° C. Zone 128   90° C. Torque 140 rpm Feed Rate 16 gm/min DieTemperature 137.8° C. Air Temperature 137.8° C. Air Pressure 50 psi Pump40 rpm

[0142] The resulting attenuated filaments (or fine fibers) of theinvention have fiber diameters ranging from 10 to 30 microns. The fibersare air laid onto a papermaking forming fabric as described in U.S. Pat.No. 4,637,859, with the fabrics of U.S. Pat. Nos. 5,857,498, 5,672,248,5,211,815 and 5,098,519, all incorporated herein by reference, alsobeing judged suitable for this purpose.

Example 13

[0143] The resultant web from the air-laying process of Example 12 istested for oil absorbency. A drop of a commercially available motor oil(SAE 20 grade, by the Society of Automobile Engineers' designation) isplaced on the web and on a commercially available paper towel,respectively, for comparison of oil absorbency. The web shows animproved oil absorbency over that of the commercial paper towel in thefollowing aspects: (1) the web absorbs oil faster than the commercialpaper towel, as shown by a shorter residence time on the surface of theweb; and (2) after 30 seconds, the web has a spot size of about 1.5 to 2times larger in diameter than that of the commercial paper towel.

Example 14

[0144] This example illustrates that the starch composition of thepresent invention can be made into building materials, e.g., pressedboard. A melt processable composition is prepared by mixing 60 wt %starch (Crystal Gum), 0.1 wt % polyacrylamide (SP2), 2 wt % urea, 2 wt %sucrose, 1.5 wt % Parez 631 NC and 34.4 wt % water (adjusted to pH 2with sulfuric acid) to form a slurry. The slurry is fed in to a torquerheometer (Model Rheocord 90) as illustrated in FIG. 1 and operatedunder the conditions as described in Example 12 above, except a singlecapillary die (having a 1 mm diameter and a temperature of 90° C.) isused instead of a melt spinning die. The extruded strand is dusted withsaw dust or wood shavings while still wet and sticky. The dusted strandsare compressed together to form a log. The log is dried at 40° C. in aforced air oven for two hours to get rid of the residual water from thestarch composition. The final product is a log of 47.8 wt % saw dust and52.2 wt % dried starch composition.

Example 15

[0145] This example illustrates that the present invention can beincorporated into structural materials as reinforcements. Though thisexample uses fibers made from a composition without high polymers. It isbelieved that when a composition of the present invention is used, theproduct would show better or equivalent performances.

[0146] A comparative cement sample is prepared as follows: 5 parts ofcommercially available Quikrete Anchoring cement are mixed with 1.5 partclean tap water until a thick syrup consistency is obtained. Within 5minutes of mixing, the cement was introduced into cylindrical molds inorder to obtain a constant dimension sample for evaluation. Thin wallmolds 5″ long and 0.23″ in inner diameter (i.e., commercially availablestraws) are filled by driving the pasty cement mixture up from thebottom. This filling method eliminates air inclusion in the finishedsample. The samples are allowed to cure for 5 days prior to evaluation.The mold is carefully scored on the outer surface so as not to damagethe sample inside, then the mold is peeled away to retrieve thecomparative sample (Example 15b).

[0147] A melt processable composition is prepared by mixing 45 wt %starch (Durabond®, available from National Starch and Chemicals Corp.,Bridgewater, N.J.), 15 wt % urea, 15 wt % sorbitol, and 25 wt % water toform a slurry. The slurry is fed in to a torque rheometer (ModelRheocord 90) as illustrated in FIG. 1 and operated under the conditionas described in Example 14 above. The fibers are about 0.02″ in diameterand are cut to 1″ in length for use herein. The extruded, thinspaghetti-like strands are incorporated into cement as follows: 5 partsof commercially available Quikrete Anchoring cement are mixed with 1.5part clean tap water and 0.5% (on a dry weight basis) starch fibers. Theadditional amount of water added herein is required to achieve thecomparable consistency as the comparative sample above. The sample moldsare filled and the samples (Example 15) are cured and retrieved in thesame manner as above.

[0148] The samples are subjectively evaluated by bending to failure byhand. Example 15 are subjectively judged to be slightly weaker than thecomparative Example 15b. Example 15 has an apparent density of 1.46g/linear inch while comparative Example 15b has an apparent density of1.48 g/linear inch. Therefore, it is demonstrated that Example 15 offersthe benefits of light weight and lower cost (on a volume basis).

Example 16

[0149] This example illustrates that the composition of the presentinvention can prophetically be made into a controlled water releasematerial when mixed with potting soil. The controlled water release isuseful for horticultural and agricultural plants which thrive in arelatively low humidity environment and/or infrequent watering. A meltprocessable composition is prepared by mixing 50 wt % starch (Durabond®,available from National Starch and Chemicals Corp., Bridgewater, N.J.),0.1 wt % polyacrylamide (SP2®), 15 wt % urea, 15 wt % sorbitol, 1.5 wt %Parez® and 18.4 wt % water to form a slurry. The slurry is fed in to atorque rheometer (Model Rheocord 90) as illustrated in FIG. 1 andoperated under the condition as described in Example 14 above. Theextruded, thin spaghetti-like strands are allowed to dry before mixingwith potting soil. The ratio of starch-based strand to potting soildepends on the requirements of various types of plants. Generally, 10 wt% of starch-based strands in potting soil shows satisfactory waterholding/release results.

Examples 17-19

[0150] Examples 17-19 use films made from compositions without thebenefit of high polymers. It is believed that when a composition of thepresent invention is used in each of these examples, the resultantproduct would show beneficial improvements in properties, e.g., lowercaliper, greater flexibility.

Example 17

[0151] This example illustrates that the compositions of the inventioncan be made into thin films, using a Werner & Pfleiderer ZSK-30co-rotating twin-screw extruder with a L/D ratio of 40. The screwconfiguration consists of four kneading sections and five conveyingsections. The extruder barrel consisted of an unheated feed zonefollowed by seven heated zones, which are designated consecutively asZones A, B, 1, 2, 3, 4 and 5. The barrel is controlled to thetemperature profile summarized below, and the screw speed is set to 150rpm. Zone A B 1 2 3 4 5 Temperature ° C. 50 50 50 95 95 95 95

[0152] A melt processable composition is prepared by metering the solidmaterials into the extruder with a K2V-T20 volumetric feeder (availablefrom K-Tron Inc., Pitman, N.J.) and metering the liquid material intoZone 1 of the extruder with a mini pump (available from Milton-Roy,Ivyland, Pa.). The components are: 44 wt % starch (Durabond® A,available from National Starch and Chemicals Corp., Bridgewater, N.J.),18 wt % urea, 18 wt % sucrose, and 20 wt % water. The mixture isconveyed from the extruder into a Zenith B-9000 gear pump into asix-inch wide flat film die (available from Killion Extruders, CedarGrove, N.J.) at a flow rate of 33 cm³/min, wherein the gear pump ismaintained at 96° C., the film die is maintained at 94° C. and the dieopening is set at 15 mils. The resultant film is extruded onto a 12-inchwide chill roll (available from Killion Extruders) which is maintainedat 37° C. The film is then wound onto a paper core at a speed of 5 fpm.The resultant film is about 1 mil in thickness, slightly tacky to thetouch, and exhibits excellent flexibility (i.e., it can be repeatedlybent at a 180 degree angle without breaking or forming a dead fold).

Example 18

[0153] This example illustrates that the film from Example 17 can bemade into a seed carrier for agricultural applications. The seed carrierfilm made according to this example provides an inexpensive materialthat can be laid down to cover and seed a large area effectively. Thematerial holds water to facilitate the germination of the seeds, and thematerial is biodegradable such that no recovery and disposal arerequired. The film of Example 17 is placed on a single-sided releasepaper and sprinkled with grass seeds available from Midwestern Supply orother garden supply stores. Another sheet of single-sided release paperis placed on top of the seeds. The assembly is placed between ¼ inch(0.635 cm) aluminum plates and inserted into a 6 inch by 6 inch (15.24cm by 15.24 cm) Carver hot press that is preheated to 207° C. Theassembly is equilibrated under low/contact pressure for one minute, thenpressure is increased to a maximum pressure of 6000 pounds. The assemblyis held under the maximum pressure for one minute and quicklydepressurized. The assembly is taken out of the press and cooled to roomtemperature. The resulting film composite shows good cohesion betweenfilm and seeds such that the film composite can be handled without lossof seeds.

Example 19

[0154] This example illustrates that the films of Example 17 are fusablesuch that the films can be made into substantially transparentbags/pouches useful as sealable food storage pouches, shopping bags,garbage bags, grocery bags, and the like. Two pieces of 4 inch by 4 inch(10.16 cm by 10.16 cm) films are overlaid with a piece of release paperinterposed between them. The release paper should be smaller than thefilms so that at least three edges of the films are in direct contactwith each other. A Vertrod impulse sealer (Model 24LAB-SP) is used toseal three sides of the overlaid films. The sealer is set at 50%voltage, 60 psi pressure, a six second dwell time (one second on and 5seconds off), and for a total sealing time of one minute. The resultantbag shows uniform, welded seals on three sides. The fourth side canoptional be sealed to form a completely sealed pouch.

Example 20

[0155] This example illustrates the water-insoluble starch compositionsof the present invention. A composition is prepared by mixing 50 wt %starch (Crystal Gum), a crosslinking additive (the type and the amountof the crosslinking additive are shown in the Table below) and a balanceof water which has been adjusted to pH 2 using sulfuric acid. Whereglyoxal (in 40% solution in water) is used, there is no need to adjustthe water pH. The composition and test sample are prepared according toTest Method for Water Solubility described hereinabove. The results areshown in the Table below: Solubility: % Additive Parez 631 Glyoxal Parez802 0.00% 37% 37% 37% 0.12% 16% 0.20% 10% 0.25% 28% 48% 0.32% 11% 0.40% 7% 0.50% 16% 16% 0.75% 14%  9% 1.00% 14%  6% 1.50% 11%  4%

[0156] The disclosures of all patents, patent applications (and anypatents which issue thereon, as well as any corresponding publishedforeign patent applications), and publications mentioned throughout thisdescription are hereby incorporated by reference herein. It is expresslynot admitted, however, that any of the documents incorporated byreference herein teach or disclose the present invention.

[0157] While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention.

What is claimed is:
 1. A substantially homogeneous compositioncomprising: (a) a starch, wherein the starch has a weight-averagemolecular weight ranging from about 1,000 to about 2,000,000; and (b) adiluent.
 2. The composition of claim 1 wherein from about 20 to about 99wt % of the starch is amylopectin.
 3. The composition of claim 1 whereinthe weight-average molecular weight of the starch ranges from about1,500 to about 800,000.
 4. The composition of claim 1 wherein thecomposition further comprises an ingredient selected from the groupconsisting of: high polymers, plasticizers and mixtures thereof.
 5. Thecomposition of claim 4 wherein the weight-average molecular weight ofthe high polymer ranges from about 800,000 to about 22,000,000.
 6. Thecomposition of claim 4 wherein a solubility parameter of the highpolymer and a solubility parameter of starch differ by less than 10MPa^(1/2).
 7. The composition of claim 4 wherein the high polymer isselected from the group consisting of polyacrylamide and itsderivatives; polyacrylic acid, polymethacrylic acid, and their esters;polyvinyl alcohol; polyethyleneimine; copolymers made from mixtures ofmonomers of the aforementioned polymers; and mixtures thereof.
 8. Thecomposition of claim 4 wherein the plasticizer comprises a hydroxylplasticizer.
 9. The composition of claim 1 wherein the compositionfurther comprises at least one additive selected from the groupconsisting of oxidation agents, cross-linking agents, emulsifiers,surfactants, debonding agents, lubricants, processing aids, opticalbrighteners, antioxidants, flame retardants, dyes, pigments, fillers,proteins and their alkali salts, biodegradable synthetic polymers,waxes, low melting synthetic thermoplastic polymers, tacktifying resins,extenders, wet strength resins, and mixtures thereof.
 10. Thecomposition of claim 4 wherein the weight-average molecular weight ofthe starch ranges from about 1,500 to about 800,000, the weight averagemolecular weight of the high polymer ranges from about 800,000 to about22,000,000, and the solubility parameter of the high polymer and thesolubility parameter of the starch differ by 10 MPa^(1/2).
 11. Thecomposition of claim 10 wherein the high polymer is selected from thegroup consisting of polyacrylamide and its derivatives; polyacrylicacid, polymethacrylic acid, and their esters; polyvinyl alcohol;polyethyleneimine; copolymers made from mixtures of monomers of theaforementioned polymers; and mixtures thereof.
 12. The composition ofclaim 1 wherein the diluent comprises a polar solvent.
 13. Thecomposition of claim 12 wherein the polar solvent is selected from thegroup consisting of: water, C₁-C₁₈ linear or branched alcohols, dimethylsulphoxide, formamide and derivatives thereof, acetamide and derivativesthereof, glycol alkyl ether and derivatives thereof, hydrazine, ammoniaand mixtures thereof.
 14. The composition of claim 12 wherein the polarsolvent comprises water.
 15. A process for preparing a substantiallyhomogeneous composition, the process comprising the steps of: (a)providing a starch having a weight-average molecular weight from about1,000 to about 2,000,000; (b) providing a diluent; and (c) mixing thestarch and diluent together to form a substantially homogeneouscomposition.
 16. The process according to claim 15 wherein the step (c)comprises the steps of feeding the starch and the diluent into anextruder, and extruding a mixture thereof.
 17. A substantiallyhomogeneous composition comprising starch and a diluent, wherein thecomposition has: (a) a melt shear viscosity of less than about 50 Pa·s;and (b) an extensional viscosity, which is at least 10 times greaterthan that of a comparative composition having no high polymer therein.18. The composition of claim 17 wherein the composition has an uniaxialdraw ratio ranging from about 5 to about
 6000. 19. The composition ofclaim 17 wherein the composition has a melting temperature ranging fromabout 80° C. to about 180° C.
 20. The composition of claim 17 whereinthe diluent comprises a polar solvent.